Type II Toxin-Antitoxin Systems in the Unicellular Cyanobacterium Synechocystis sp. PCC 6803

Toxins (Basel). 2016 Jul 21;8(7):228. doi: 10.3390/toxins8070228.


Bacterial toxin-antitoxin (TA) systems are genetic elements, which are encoded by plasmid as well as chromosomal loci. They mediate plasmid and genomic island maintenance through post-segregational killing mechanisms but may also have milder effects, acting as mobile stress response systems that help certain cells of a population in persisting adverse growth conditions. Very few cyanobacterial TA system have been characterized thus far. In this work, we focus on the cyanobacterium Synechocystis 6803, a widely used model organism. We expand the number of putative Type II TA systems from 36 to 69 plus seven stand-alone components. Forty-seven TA pairs are located on the chromosome and 22 are plasmid-located. Different types of toxins are associated with various antitoxins in a mix and match principle. According to protein domains and experimental data, 81% of all toxins in Synechocystis 6803 likely exhibit RNase activity, suggesting extensive potential for toxicity-related RNA degradation and toxin-mediated transcriptome remodeling. Of particular interest is the Ssr8013-Slr8014 system encoded on plasmid pSYSG, which is part of a larger defense island or the pSYSX system Slr6056-Slr6057, which is linked to a bacterial ubiquitin-like system. Consequently, Synechocystis 6803 is one of the most prolific sources of new information about these genetic elements.

Keywords: PIN-domain; RNA degradation; RNA interferase; RNA turnover; VapC; bacterial toxins; cibonuclease; cyanobacteria; hydrogenase; toxin–antitoxin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antitoxins / genetics
  • Antitoxins / metabolism*
  • Bacterial Toxins / genetics
  • Bacterial Toxins / metabolism*
  • Chromosomes, Bacterial
  • Gene Expression Regulation, Bacterial
  • Gene Expression Regulation, Enzymologic
  • Protein Domains
  • RNA Stability
  • RNA, Bacterial / metabolism
  • RNA, Messenger / metabolism
  • Ribonucleases / genetics
  • Ribonucleases / metabolism*
  • Structure-Activity Relationship
  • Synechocystis / enzymology*
  • Synechocystis / genetics
  • Synechocystis / growth & development
  • Time Factors


  • Antitoxins
  • Bacterial Toxins
  • RNA, Bacterial
  • RNA, Messenger
  • Ribonucleases